Lymphokines are involved in the cell-to-cell communication of immunologically reactive cells. Lymphocytes, when stimulated, release products such as T Cell Growth Factor (TCGF), Macrophage Migration Inhibition Factor (MIF), and Macrophage Activation Factor (MAF). TCGF (also known as Interleukin 2) is being studied for its ability to perpetuate cytotic T-Lymphocytes which can be cloned for cytotoxic capability against specific tumor cells. Using TCGF, cytotoxic cells generated in vitro are being tested for their capability of influencing tumor growth in vivo. MIF is being studied for its ability to localize tumor-reactive macrophages at tumor sites. MAF is being studied for its macromolecular effects on macrophages and for its ability to activate macrophages to kill neoplastic cells. Novel approaches for the production and purification of lymphokines are being evaluated.